Extraction of aromatics with aluminum halide-aromatic complexes



Patented Sept. 13, 1949 UNITED STATES PATENT YOFFICE EXTRACTION FAROMATICS WITH ALU- MINUM HALIDE -AROMATIC COMPLEXES Ware ApplicationJanuary 2, 1947, Serial No. 719,754

(Cl. 1mi-14.25.)

7 Claims.

The present invention is concerned with the separation of oils intotheir relatively more. aro-v matic constituentsand into their relativelymore paranic and naphthenic constituents. The inventionf is--moreparticularly concerned with the.

treatmentot petroleum oils, especially petroleum oils boiling. in thenaphtha, kerosene and gas oil range, with a solvent selectedfrom. a newclass of solvents which have been found to give particularly desirableresults. Ihesolvents of the present invention are selected from theclass of aluminum halide-aromatic hydrocarbon complexes.

It isf.' known in the art to treat oils, particu-V nitrobenzene,aniline, beta. beta dichlor diethyl.

ether, andthe like. Solvent mixtures of these solvents are employedaswell as other substances having. theability tomodify. the selectivityand solvent power of theparticular solvent or solvent mixture.Substances of. this type are water, liqueedinormally gaseoushydrocarbonssuch as propane .'andnbutane, as Well. as-.alcohols and glycols. The oiland th-esolvent, or'solvent mixture, employed are contacted by variousmethods, asfor example, by. a batcl'i'or. by. asemi-batch operation.However, the usualmethodemployedis acountercurrentitower. treatingoperation. .In this opera.- tion, the lighterxphase, usually the oil, isintroducedatthe lower or middle section of acountercurrentitreatingtower. The-heavier phase, usually the solvent,.is` introduced into the upper partioffthe countercurrent solventtreating tower.v

The respective phases low countercurrently under, conditions in whichcomplete contact betweenthevrespective phases is secured This isusuallyaccomplished by suitable distributing and contacting means.Temperature and. pressure conditions arefmaintainedion-the systemadapted t0. secureftheformationof. a solvent-rich or ex tract- -phaseandthe formation of a relatively solventfpoor, or. raffinate phase. Therespective phases. are removedfrom the tower. andthe solvent-separatedby.,v anyV suitable means, such as by, distillation, washing, andthelike. For commercial solvent4 treating yprocesses it has beenvdifficult to find a solvent which is entirely suit'.-

2. able in all respects. Anideal solvent is one which willmake a clearseparation between the aromatic and the paraiiinic constituents of theoil and which will also extract substantially the entire quantity ofaromatic constituents present. It is also desirable to have the solventexhibit this preferential selectivity at. relatively low temperatures inorder'toreduceoperating diculties and expenses. Furthermore; itisdesirable that the selective solvent bereadily and economicallyremovable from the extract and` rainate phases. The selective solventisf usually: separatedv from the rannate and extract phases byre-extracting said phaseswitha secondaryrsolvent or'by distillation. Ifdistillation be employed to separate the solvent from the oil, itisnecessary that a suicient differencev exist with. respect to the variousboiling'points.. Solvent-.recovery from the respectivephases,-particularly from the extract phase, will be greatly facilitatedprovided the particular solvent employed is completely miscible with therelatively more aromaticy fraction at operating temperature, whichtemperature should not be excessively.v above atmospheric temperaturesdue to heat economies, and providing the solvent tends towardimmiscibility with the extract at temperature notV substantially belowatmospheric temperatures.

We have now discovered a class of solvents which possess theseidesirablecharacteristics and which are therefore particularly. desirable in thecommercial solvent treatment of petroleum oils. The solvents ofourinvention are selected from the class of substances commonlydesignated as aluminum. halide-aromatic. hydrocarbon. complexes.Examplesfofour particular class of solvents arealuminum,chloride-benzene, aluminum chloridefxylenea.

y AlzCla-toluene-compl'ex is prepared in the fol lowingmanner;'powdered-A1013isagitated in an excess of toluene atapproximately'l' to 200CAA F., while a promotersuch yasiethylk chlorideor- HC1 saturated with4 'H20l vaporis slowly bubbled through themixture; rlllfiisoperation is'continued until all, or essentially all,solid AlCls disappears and is replaced with a liquid layer of thecomplex. The reaction generally takes about 4 6 hours. After thereaction is complete, the complex may be separated from supernatanttoluene, and prepared for further use by extraction with a paraffin.

Our invention may be stated briefly as follows:

Aluminum chloride forms a complex with toluene in the proportion .ofAl2Cl.lC'zI-I8. In other words, this complex is a complex of twoaluminum chloride molecules with one molecule of toluene. Now thiscomplex is capable of talring on or absorbing additional toluene untilit forms a Saturated complex with the composition AlzCle-.GCvHa We havefound that a reversible reaction of aluminum chloride with toluene andwith aromatics in general can therefore heem-` ployed as the means ofrecovering the aromatics from their mixtures with other hydrocarbons. Inthe specific application to the recovery of toluene, for example, from avirgin naphtha, the reaction of aluminum chloride with an excess oftoluene results in theformation of the saturated complex AlaClaC'zH.This saturated complex can then be dearomatized to as low as a 1 to 1mol ratio toluene/AlzCls, and the resulting dearomatized complex, havinggreat afnity toward toluene can be employed in recovering additionalamounts of the aromatic from the feed. Theoretically, this cycle can berepeated indefinitely. The dearomatization, or the regeneration of thesolvent can be accomplished either by distillation, preferably underreduced pressure, or by extracting the excess toluene with a paraffinicsolvent of different boiling range from the toluene which can then beseparated from the toluene by distillation. We have found the lattermethod of regeneration to be considerably more advantageous sincetoluene is disproportionated to an .i

appreciable extent when the complex is decomposed by heat.

Nature of solvent comples.` composition It has been suggested that thesaturated AlzCls-toluene complex has the following structure:

The following cycle of reactions, using aluminum chloride-toluenevcomplex as an example, illustrate the principle involved in theformation of the complex and its function in the solvent process:

The cycle illustrated by the last two equations can be repeatedindefinitely in the extraction .of toluene or other aromatics,regeneration of the solvent by partial dearomatization, and recyclingthe regeneratedsolvent back to the reaction zone. Good recoveries ofaromatics can be obtained in the process. The products are exceptionallypure. The following example is typical of the results obtained whenextracting toluene from heptane-toluene blends:

Eesti-action of toluene from a 50 mol percent blend in N-heptane with acomplex dearomatieed to 1.5/1 toluene to AlzCls mol ratio at 70 F.,atmos. pressure, and 1 hr. contact time Mol Per Cent Toluene in Feed 50Mols Toluene in Feed 0. 21 Original Complex:

Toluene/AlzCl Mol Ratio 1. 5 Mols Complex 0.49 0.37 0. 25 0. 25 MolsToluene Required to Form Saturated Complex (AlzCle-C-l'HB) 2.21 1.671.13 1.13 Product:

Final Complex, Toluene/A1201.; Ratio..- 1.'93 2.08 2.28 2.28 TolueneExtracted from Feed, Mols 0.21 0.21 0.20 0. 20 Toluene Recovery fromFeed, Mol Per Cent 95 95 Toluene Purity, Per Cent "7"--. 95 95 '95 Inthe course of our experimental investigation of this process we havediscovered that the composition .of the complex and therefore itssolvent capacity, is a direct function of the concentration of aromatichydrocarbon material in equilibrium with it. The following dataillustrate the effect .of the composition of the hydro-V carbonmaterial, i. e., the raffinate, on the cornj position of the complex inequilibrium with it.

Studies on the equilibrium between AlzCls-toluene complex and variousblends of toluene and heptane; runs made at 70"V VF. and atmos.pressure, 10 min. contact time Composition of Original ComplexAlzClu-CyHa Wt. of Complex Employed 40 The fact that an equilibrium isestablished between the complex and raffinate points to the feasibilityof countercurrent .operation of the extraction process. Batch orconcurrent operation is inadvisable since a complex of any initialsaturation Would come to an equilibrium with the raffinate, and very lowlrecoveries would be ob.

tained unless prohibitively large amounts of the solvent were employed.The countercurrentextraction can be conveniently Ycarried out in apacked column, a series of agitators and settlers,

or any other commonly employed equipment fo extraction.

Y ItV has also been determined by experimental work that the complexcombined with the extracted aromatics, also contains traces of v othervhydrocarbons dissolved from the feed. v`These must be eliminated fromthe final product Vin order to obtain pure aromatics. An advantageousand simple method of accomplishing this is by countercurrentlywashing'the extract 'in pure aromatics. This does not impose additionalload on the solvent capacity since the solvent in equilibrium with theentering feed does not reachY saturation unless the washing step isemployed.

We prefer to operate the .extraction and washing towers at atmosphericto 50'pounds psig. and

at temperatures from about 50 F. to about 250 F. Complex regeneration,as will be explained more fully below, if carried out by distillation,is

conducted at approximately 0.25 atmosphere ab-` solute. Ifcountercurrent washing with'a para'irr` hydrocarbon is used for complexregeneration, l* this step is carried out at the same conditions as theextraction.

Ertractzon system process sary to vaporize the hydrocarbon extract phasein an amount approximately twicet-hat ofthe feed. The processr of, ourinvention may be readily understood by referencetothe attacheddrawing,illustrating one modification ofthe same:

Dry and olen-free feed: containing weight per cent toluene through linel enters the .middle of the. extraction towerZ', inthiscase containingfive extraction stages, where. it is. contacted with the downowingsolvent complex, entering through. line 3. The rainate, which issolventfree and contains 2 weight .percent toluene, is released at thetop of. the .tower through line 4. The extract phase is released throughline 5to-the top of solvent recovery. tower 6 where the solvent isregenerated by countercurrent washing with a paraffinic extraction.agent `such as kerosene which enters thebottomfofl the solvent recoverytower through line'l-from; line I4. The regenerated solvent is removedfrom the bottom of the tower through line 8 and is returned to theextraction tower through 1ins-.3: vlViMse-up.solvent is added throughline l5. The solution of solventfree extract in kerosene is takenoverhead from tower 6 through line Sand emptied into fractionator l0; inwhich it is distilled in order to recover kerosene as bottoms.. throughline Il and the final toluene extract is` taken overhead through lineI2, condensed in condenser 1.6 andled to a storage vvessel not shown. Aportion of the toluene overhead is withdrawn through line I 3A andreturnedto theextraction tower-.as reux to wash traces of otherhydrocarbonsdissolved fromthe feed from the extract.

For the extraction of 100 lbs. feed, in order to produce 18.75 lbs. of98 weight percent pure toluene and 81.25 lbs. of raiinate containing 2weight percent toluene, a solvent circulation of 300 lbs. is necessaryunder the conditions described in the flow diagram. This represents 91.8weight percent toluene recovery and 1.65/1 solvent/oil volume ratio. Aconsiderable amount of reflux must be returned to the extract end of thesystem in order to obtain this product purity with 21/2 theoreticalstages below the feed inlet point. In the stripping and enrichingsections, 201 lbs. of reux phase must be returned. Solvent regenerationis conducted in a tower With ve theoretical stages. With this number ofstages, the extract phase must be washed with 520 lbs. of kerosene inorder to recover 99 weight percent of the extracted toluene.

The extraction is 4preferably carried out in a countercurrent manner atatmospheric pressure and preferably at temperatures in a vicinity ofroom temperature, that is, approximately '70 F.

Aside from the low stage and solvent requirements, the aluminumhalide-aromatic complex solvent system requires a minimum temperaturecontrol, no refrigeration and no pressure equipment.

Regeneration of spent solvent comples:

It has been found that the AlzClG-toluene complex can be dearomatized,that is, regenerated to 1:1 toluene AlzCle mol ratio either by acountercurrent extraction with a paraflinic.s'olventforby distillationunder reduced pressure. The regen-.. erated complex can then besaturatedagain with additional amounts of toluene.

in spite of the fact that it introduces an additionaly step into thesolvent recovery process, that is, theI separation by distillation ofthe nal toluene` product and the extracting medium. This is `due. to thefact that the decomposition of the product complex with heat results ina partial disproportionation of toluene. The extent of thisdisproportionation is illustrated in the following sum-Y mary of dataobtained when decomposing the complex under 20 ofr vacuum andtemperaturesas high as 165-175o F.

Regeneration of AZzCZs.6C7Hs Complex,l

Method of Regeneration HC Phase Distil- Extraction Composition lationwith nCvHxt* Benzene, Vol. percent 2. 5 0 Trluene, Vol. percent 75. 3100 Higher Aromatics, Vol. percent 22. 2 0( *Heptane free basis.

It would be expected that the use of distillation' for the regenerationofA complexes between A12C1s4 and 08+ aromaticsJ would result in a stillhigherdegree of disproportionation or isomerization.

Our preferred solvent regeneration processcomprises the extraction ofthe saturated-or par.

p of toluene concentration in the hydrocarbonmaa terial in equilibriumwith the complex. |Ihis is, illustrated by the following data which wereob. tained in a series of experiments in which the saturatedAlgClaCvI-Ia complex was agitated at room temperature and atmosphericpressure with toluene heptane blends of varying compositions:

Regeneration of .llzCls-toluene` complex by ea'- tractz'on with heptaneand blends of heptane in toluene operation at 70 F., atmosphericpressure, and 10 min. contact time.

Wt. of Complex Employed 40 gms. of AlzCls-6C1H5 Mols of Complex 0. 049

A complex of any desired composition can be obtained by the methoddiscovered by us merely by adjusting the toluene content of theextraction medium. The data cited illustrate the use of heptane as theextraction medium. Other parafns, however, are equally good.Commercially, it may be preferable to use hexane or even pentane whichcan be easily separated from the extracted toluene by distillation.

The extracting agent employed will produce a variation in the operationof fractionator l0. With light paraiiin hydrocarbon extracting agentssuch as pentane, hexane and heptane, toluene is recovered as bottoms infractionator I 0 while the light hydrocarbons are recovered overhead.With heavier paralin hydrocarbons, e. g., kerosene, fractionator Itoperates as de.

The. regenerate.. tion, by means of extraction,- is moreadvantageousscribed inthe drawing with the toluene taken overhead andthe kerosene removed as bottoms.

It is to be noted that a feedstock from which aromatic hydrocarbons aretobe extracted with our aluminum halide-aromatic hydrocarbon complex maycontain one or more aromatic hydrocarbons, e. g., benzene, toluene,xylene isomers, trimethylbenzenes, etc. In this event, the aluminumhalide-aromatic hydrocarbon complex will form with one or more of thesematerials produ-cing a mixed extract containing materials such asaluminum halide-toluene-benzene, or aluminumhalide-toluene-trimethylbenzene in which part of the aluminum halidescomplex saturation is satisfied by toluene and part by the otheraromatic hydrocarbons; e. g., Al2Cls-2 toluene-4 xylene.

Although the invention has been described chiefly by explaining thesolvent process using aluminum chloride-toluene as the solvent, nointention is made to limit the invention thereto, and it is to beunderstood that the process is completely operable employing otheraluminum hal- 'ides with other aromatic hydrocarbons or mixed aromatichydrocarbons.

Having thus described the invention, what is claimed is:

1. A continuous process for extracting aromatic hydrocarbons fromhydrocarbon mixtures of aromatic and non-aromatic hydrocarbons whichcomprises subjecting said mixtures to contact in an extraction zone withan aluminum halidearomatic hydrocarbon complex containing two mols ofaluminum halide and at least one mol of aromatic hydrocarbon, removingfrom the extraction zone an aluminum halide-aromatic hydrocarbon complexof increased aromatic hydrocarbon content containing two mols ofaluminum halide and up to six mols of laromatic hydrocarbon, passing thecomplex ofV increased aromatic content to a regeneration zone anddecomposing the complex of increased aromatic content in theregeneration zone to recover aromatic hydrocarbons therefrom andregenerate the aluminum tent is regenerated by distillation underreduced Y pressure.

4. A method according to claim 1 in whichV the complex of increasedaromatic hydrocarbon content is regenerated by extraction with anon-aromatic hydrocarbon boiling at a temperature different from thearomatic hydrocarbon being extracted. Y

5. A process according to claim 1 in which the solvent extractionoperation is' carried outcoun'- tercurrently.

6. A process according to claim 1 in which the extraction is carried outat atmospheric pressure.

and temperatures in the neighborhood of room temperature.

7. A process according to claim 1 in which said solvent is recoveredfrom the respective phases by distillation under reduced pressure. Y

- PHILETUS H. HOLT, II. n NICHOLAS'MENSHIH.

REFERENCES CITED Y The following references are of record in the le ofthis patent:

UNITED VsTATiirs PATENTSy Y Number Name Date 2,079,885 Voorhees Q. May11, 1937 2,081,720 Van Dijck May 25, 1937 v2,114,524 Egli Apr. 19, 193782,138,832 Brown et a1 Dec. 6, V1938 2,257,086 AtWell Sept. 30, 19412,260,279 DOuville et al Oct. 21, 1941 2,382,445

Ross et al. Aug. 14, 1945

